Finally bought it on Steam since I've been Nintendo-only until my 2016 PC could finally pull off 7th gen graphics reliably.
The good:
-Variation and tasting the gimmicks of each of the games you're passing through. A small taste of Wisp power, a little bit of wall-jumping or light-speed dash. Part of classic Sonic's appeal, to me, was gimmicks that came and went before they outstayed their welcome. You missed the depth of a really refined system that way, but polish was *never* the franchise's strong suit, even if the early games are largely very sound, and you have fun constantly experiencing bits of new things, mastering them over the course of a stage before you move on to the next thing.
-Reinventing the modern stages in the Genesis style. This feels like the most original contribution of the game, while the Genesis-era Act Two stages are just okay, the post-Genesis Act One stages take the greater scale of the 3D games and throw them into a the 2D space creating something that feels very fresh. Getting chased by the truck in City Escape Act 1 had a certain thrill to it that went beyond mere nostalgia.
-The adventures of Eggman and Eggman.
Whatever they pay Mike Pollock, it's not enough.
The middling:
Stage choice. It's going to be a magnet because everyone's going to have their own Sonic Generations Choice lineup. There are some great choices, but the game's tendency to lean on early-game stages holds it back, notably City Escape *and* Seaside Hill being back to back raises an eyebrow, especially when both games have a few stages that are more iconic. I give them props for Crisis City (for giving you just the taste of Sonic '06, lord knows that's all you need), for Planet Wisp being beautiful and clever, and for Sky Sanctuary being one of the underappreciated Sonic 3 & Knuckles stages (though not the best choice).
For my money:
Sonic 1 - Green Hill
Sonic 2 - Chemical Plant
Sonic 3 & Knuckles - Flying Battery
Sonic Adventure - Lost World
Sonic Adventure 2 - Green Forest
Sonic Heroes - Bullet Station
Sonic '06 - Crisis City
Sonic Unleashed - Chun-Nan
Sonic Colors - Planet Wisp
Sonic 1 - Green Hill
Sonic 2 - Chemical Plant
Sonic 3 & Knuckles - Flying Battery
Sonic Adventure - Lost World
Sonic Adventure 2 - Green Forest
Sonic Heroes - Bullet Station
Sonic '06 - Crisis City
Sonic Unleashed - Chun-Nan
Sonic Colors - Planet Wisp
The extra challenges: these are scattershot. Some like the elemental shield challenge or the one where you chase Espio around Speed Highway were inventive and fun, some are just there, and the doppelganger races have no element of interactivity to them, disguised timer challenges.
The bad:
The running theme of this is that the game is undercooked.
Most of us were around to see the decline and fall of Sega, but the fall was a long fall and in several phases, from the end of the Dreamcast they still trucked along as a broad-based publisher with a lot of good ideas through the end of the 6th generation, but then the 7th gen dawned and there was the disaster of Sonic '06. Okay, they right the ship with Sonic Unleashed, a big-budget game with a repetitive Werehog mechanic and thrilling if kind of shallow daytime stages. But along came Sega's financial straits of 2011, the one that got Bayonetta 2 initially cancelled where Sega cut back drastically on their publishing business. This game was probably far enough along the pipeline that it shouldn't have been effected by that, but it clearly was.
It's just too short, and other elements of it come up skimpy, like the weak bonus content (the art gallery is egregiously bare-bones compared to what it could have been) a short game, and a number of stages befitting a Genesis game, and you have to wonder if the game's anemia in so many respects is due to a lack of budget.
But it's odd in that regard because other post-Unleashed games feel meatier, like Sonic Colors or even Lost World. More well-realized and whole. What made it into the game feels complete, but the game itself feels like a shadow of what it could have been. To speak to the thread title: it feels like right when you're getting in the groove of playing the game, around Planet Wisp and the Egg Dragoon, it's over. Sonic does not have enough runway.